Hei Guys,
I need to apologise for leading you all up the garden path because as most of you will know what I posted was crap.

At the time of writing that I hadn't actually looked at the lathe, but I was going on information received from someone at a shop who obviously knows less than I do - in fairness I will say that it must be bloody hard to keep up to date on every bit of kit.

Anyway, the problem with the head lifting turned out to be a missning spring pin that acts as a locater on the jaws that lock down the head to the swivel base.
Got the offending pin from Repco and all is well.
Cheers and apologies